There have been ash-free coals obtained by removing ash from coals. Patent Literature (PTL) 1 discloses a customary method for producing an ash-free coal. The ash-free coal production method produces the ash-free coal by mixing coal with a solvent; removing solvent-insoluble ash from a coal component dissolved in the solvent (soluble coal component) to leave a solution containing the soluble coal component in the solvent; and removing the solvent firm the soluble coal component (from the solution).
PTL 1 describes a technique for improving the settling velocity of a solvent-insoluble component by blending general coal with caking coal (e.g., claim 1 and paragraph [0008] in PTL 1).
Suitable fluidity (thermoplasticity) of an ash-free coal varies depending on the intended use thereof. The use is exemplified by coal for coke making and a fuel typically for a boiler. Fluidity control is important particularly when the ash-free coal is used as coal for coke making.